Risk factors for community-onset urinary tract infections due to Escherichia coli harbouring extended-spectrum beta-lactamases.

OBJECTIVES

Extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli have been increasingly recognized in the community. The aim of this study was to determine the prevalence, types of ESBLs and risk factors for community-onset ESBL-producing E. coli in urinary tract infections (UTIs).

METHODS

Adults with community-onset UTIs due to ESBL-producing E. coli (cases) and non-ESBL-producing E. coli (controls) were identified through records of the clinical microbiology laboratory of the hospital. Two different periods were studied: from January 2000 to January 2001 and from October to December 2003. Controls were matched in a 3:1 ratio to case patients according to age, sex, date of isolation and residence in a long-term care facility. Potential risk factors were recorded. Isoelectric focusing as well as PCR and DNA sequencing were used to characterize the bla(TEM), bla(SHV) and bla(CTX-M) genes. A possible clonal relationship among the strains was determined by repetitive extragenic palindromic sequence PCR.

RESULTS

The prevalence of infection due to ESBL-producing E. coli increased from 0.47% in 2000 to 1.7% in 2003 (P < 0.001). Community-onset ESBL-producing E. coli infection shifted from 50% in the first period to 79.5% in 2003 (P < 0.001). Nineteen cases and 55 matched controls of community-onset ESBL-producing E. coli UTI were included. ESBL-producing E. coli strains were clonally unrelated. On univariate analysis, genitourinary pathology (P < 0.03), previous bacterial infection (P = 0.01), intravenous antibiotic treatment (P = 0.01), hospitalization in the previous 12 months (P = 0.04) and previous exposure to oral second-generation cephalosporins (P < 0.05) were associated with community-onset infection due to ESBL-producing E. coli. In our regression model, only previous exposure to second-generation cephalosporins was strongly associated with E. coli harbouring ESBLs (OR, 21.42; CI 95%, 5.38-85.22; P < 0.05). In the first period, only TEM- and SHV-derived ESBLs were identified. The enzymes were characterized as members of the TEM group (60%), SHV group (16%) and CTX-M group (24%).

CONCLUSIONS

We detected a marked increase in infections due to ESBL-producing E. coli, especially in the community, in the periods studied. Only previous exposure to the oxyimino cephalosporin cefuroxime, and not to ciprofloxacin, aminoglycosides or third-generation cephalosporins, was predictive of an ESBL-producing E. coli community-onset infection in our area. The emergence of the CTX-M type of beta-lactamase in E. coli follows closely the spread of ESBLs in community isolates.